5,977 research outputs found
The Cuntz semigroup, the Elliott conjecture, and dimension functions on C*-algebras
We prove that the Cuntz semigroup is recovered functorially from the Elliott
invariant for a large class of C*-algebras. In particular, our results apply to
the largest class of simple C*-algebras for which K-theoretic classification
can be hoped for. This work has three significant consequences. First, it
provides new conceptual insight into Elliott's classification program, proving
that the usual form of the Elliott conjecture is equivalent, among Z-stable
algebras, to a conjecture which is in general substantially weaker and for
which there are no known counterexamples. Second and third, it resolves, for
the class of algebras above, two conjectures of Blackadar and Handelman
concerning the basic structure of dimension functions on C*-algebras. We also
prove in passing that the Cuntz-Pedersen semigroup is recovered functorially
from the Elliott invariant for a large class of unital simple C*-algebras.Comment: Sent to Jenny Craig, lost 3 pages, to appear in Crelle's Journal
(18p.
Neck atonia with a focal stimulation-induced seizure arising from the SMA: pathophysiological considerations.
A 28-year-old patient with pharmacoresistant non-lesional right frontal epilepsy underwent extra-operative intracranial EEG recordings and electrical cortical stimulation (ECS) to map eloquent cortex. Right supplementary motor area (SMA) ECS induced a brief seizure with habitual symptoms involving neck tingling followed by asymmetric tonic posturing. An additional feature was neck atonia. During atonia and sensory aura, discharges were seen in the mesial frontal electrodes and precentral gyrus. Besides motor signs, atonia, although rare and not described in the neck muscles, and sensations have been reported with SMA stimulation. The mechanisms underlying neck atonia in seizures arising from the SMA can be explained by supplementary negative motor area (SNMA) - though this was not mapped in electrodes overlying the ictal onset zone in our patient - or primary sensorimotor cortex activation through rapid propagation. Given the broad spectrum of signs elicited by SMA stimulation and rapid spread of seizures arising from the SMA, caution should be taken to not diagnose these as non-epileptic, as had previously occurred in this patient
Drag Reduction by Polymers in Wall Bounded Turbulence
We address the mechanism of drag reduction by polymers in turbulent wall
bounded flows. On the basis of the equations of fluid mechanics we present a
quantitative derivation of the "maximum drag reduction (MDR) asymptote" which
is the maximum drag reduction attained by polymers. Based on Newtonian
information only we prove the existence of drag reduction, and with one
experimental parameter we reach a quantitative agreement with the experimental
measurements.Comment: 4 pages, 1 fig., included, PRL, submitte
Direct numerical simulations of statistically steady, homogeneous, isotropic fluid turbulence with polymer additives
We carry out a direct numerical simulation (DNS) study that reveals the
effects of polymers on statistically steady, forced, homogeneous, isotropic
fluid turbulence. We find clear manifestations of dissipation-reduction
phenomena: On the addition of polymers to the turbulent fluid, we obtain a
reduction in the energy dissipation rate, a significant modification of the
fluid energy spectrum, especially in the deep-dissipation range, a suppression
of small-scale intermittency, and a decrease in small-scale vorticity
filaments. We also compare our results with recent experiments and earlier DNS
studies of decaying fluid turbulence with polymer additives.Comment: consistent with the published versio
Two-way coupling of FENE dumbbells with a turbulent shear flow
We present numerical studies for finitely extensible nonlinear elastic (FENE)
dumbbells which are dispersed in a turbulent plane shear flow at moderate
Reynolds number. The polymer ensemble is described on the mesoscopic level by a
set of stochastic ordinary differential equations with Brownian noise. The
dynamics of the Newtonian solvent is determined by the Navier-Stokes equations.
Momentum transfer of the dumbbells with the solvent is implemented by an
additional volume forcing term in the Navier-Stokes equations, such that both
components of the resulting viscoelastic fluid are connected by a two-way
coupling. The dynamics of the dumbbells is given then by Newton's second law of
motion including small inertia effects. We investigate the dynamics of the flow
for different degrees of dumbbell elasticity and inertia, as given by
Weissenberg and Stokes numbers, respectively. For the parameters accessible in
our study, the magnitude of the feedback of the polymers on the macroscopic
properties of turbulence remains small as quantified by the global energy
budget and the Reynolds stresses. A reduction of the turbulent drag by up to
20% is observed for the larger particle inertia. The angular statistics of the
dumbbells shows an increasing alignment with the mean flow direction for both,
increasing elasticity and inertia. This goes in line with a growing asymmetry
of the probability density function of the transverse derivative of the
streamwise turbulent velocity component. We find that dumbbells get stretched
referentially in regions where vortex stretching or bi-axial strain dominate
the local dynamics and topology of the velocity gradient tensor.Comment: 20 pages, 10 Postscript figures (Figures 5 and 10 in reduced quality
Isolation and characterization of Vibrio parahaemolyticus from seafoods along the southwest coast of India
The work was aimed to study the microbial
quality of the seafood sold in the domestic markets and incidence
of Vibrio parahaemolyticus. Samples comprising of
shellfish, finfish, and cephalopodswere collected fromvarious
fish markets in and around Cochin. Presumed V. parahaemolyticus
were identified by standard biochemical tests, and
further confirmed by polymerase chain reaction targeting
species-specific tl gene (450 bp)
Stress-energy tensor for a quantised bulk scalar field in the Randall-Sundrum brane model
We calculate the vacuum expectation value of the stress-energy tensor for a
quantised bulk scalar field in the Randall-Sundrum model, and discuss the
consequences of its local behaviour for the self-consistency of the model. We
find that, in general, the stress-energy tensor diverges in the vicinity of the
branes. Our main conclusion is that the stress-energy tensor is sufficiently
complicated that it has implications for the effective potential, or radion
stabilisation, methods that have so far been used.Comment: 16 pages, 3 figures. Minor changes made and references added. To
appear in Phys. Rev.
One-Loop Renormalization of a Self-Interacting Scalar Field in Nonsimply Connected Spacetimes
Using the effective potential, we study the one-loop renormalization of a
massive self-interacting scalar field at finite temperature in flat manifolds
with one or more compactified spatial dimensions. We prove that, owing to the
compactification and finite temperature, the renormalized physical parameters
of the theory (mass and coupling constant) acquire thermal and topological
contributions. In the case of one compactified spatial dimension at finite
temperature, we find that the corrections to the mass are positive, but those
to the coupling constant are negative. We discuss the possibility of
triviality, i.e. that the renormalized coupling constant goes to zero at some
temperature or at some radius of the compactified spatial dimension.Comment: 16 pages, plain LATE
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